Heteroatom substituted benzoyl derivatives that enhance synaptic responses mediated by AMPA receptors

ABSTRACT

Compounds                    
     are useful for enhancing synaptic responses mediated by AMPA receptors are disclosed, as are methods for the preparation thereof and methods for their use for treatment of subjects suffering from impaired nervous or intellectual functioning due to deficiencies in the number of excitatory synapses or in the number of AMPA receptors. The invention compounds can also be used for the treatment of non-impaired subjects for enhancing performance in sensory-motor and cognitive tasks which depend on brain networks utilizing AMPA receptors and for improving memory encoding.

This application is a division of application Ser. No. 08/461,235, filedJun. 5, 1995 now U.S. Pat. No. 5,891,876, which is a division ofapplication Ser. No. 08/374,584, filed Jan. 24, 1995 now U.S. Pat. No.5,747,492, which is a 371 of PCT/US93/06916, filed Jul. 23, 1993.

This invention was made with United States Government support underGrant No. AFOSR 89-0383, awarded by the Air Force Office of ScientificResearch. The United States Government has certain rights in theinvention in the United States.

FIELD OF INVENTION

The present invention relates to novel compounds which are useful, forexample, in the prevention of cerebral insufficiency, to enhancereceptor functioning in synapses in those brain networks responsible forhigher order behaviors, and the like. In a particular aspect, theinvention relates to methods for the use of the compounds disclosedherein, and to methods for the preparation thereof.

BACKGROUND OF THE INVENTION

Excitatory synaptic currents at many (probably most) sites intelencephalon (cortex, limbic system, striatum; about 90% of humanbrain) and cerebellum occur when the transmitter glutamate is releasedby input axons onto what are usually referred to as theα-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA), orAMPA/quisqualate, receptors. Drugs that enhance these receptor currentswill facilitate communication in brain networks responsible forperceptual-motor integration and higher order behaviors. It is alsoknown from the literature (see Arai and Lynch in Brain Research, inpress) that such drugs will promote the formation of long-termpotentiation, a physiological effect widely held to encode memory.

For example, Ito et al., J. Physiol. Vol. 424:533-543 (1990), discoveredthat aniracetam, N-anisoyl-2-pyrrolidinone, enhances AMPA receptormediated currents without affecting currents generated by other classesof receptors. Unfortunately, however, the drug is effective only at highconcentrations (˜1.0 mM) applied directly to the brain. The low potency,limited solubility, and peripheral metabolism of aniracetam limit itsutility as an experimental tool and its potential value as atherapeutic. There is a need, therefore, for the design and synthesis ofnew drugs that are more potent, more soluble and less readilymetabolized than aniracetam. Such compounds would provide new tools formanipulating the properties of the AMPA receptor and would be a majorstep towards a drug that could enhance AMPA receptor function in thebrain after peripheral administration.

BRIEF DESCRIPTION OF THE INVENTION

We have discovered novel compounds that are several times more potentthan aniracetam in enhancing synaptic responses (i.e, they producelarger effects than aniracetam at lower concentrations). The inventioncompounds increase the strength of long-term potentiation and increasesynaptic responses in the brain following peripheral administration.Invention compounds can be used, for example, to facilitate behaviorsdependent upon AMPA receptor, as therapeutics in conditions in whichreceptors or synapses utilizing them are reduced in numbers, and thelike.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows that Invention Compound I(1-(1,4-benzodioxan-5-ylcarbonyl)-1,2,3,6-tetrahydropyridine;alternatively referred to asN-(3,4-ethylenedioxy)benzoyl-1,2,3,6-tetrahydropyridine) increases theamplitude and duration (measured as half-width) of synaptic responses inthe field CA1 in in vitro slices prepared from rat hippocampus. Theseresponses are known to be mediated by AMPA receptors [Muller et al.,Science Vol. 242: 1694-1697 (1988)]. Note that Invention Compound I at750 μM has a much larger effect than does aniracetam at twice theconcentration (1500 μM). Note also that the effects occur quickly afterinfusion (horizontal bar) and reverse upon washout.

FIG. 2 compares the effects of three invention compounds; i.e.,Invention Compound I (i.e.,1-(1,4-benzodioxan-5-ylcarbonyl)-1,2,3,6-tetrahydropyridine), InventionCompound II (i.e., 1-(1,3-benzodioxol-5-ylcarbonyl)-piperidine);alternatively referred to as (N-(3,4-methylenedioxybenzoyl)piperidine,and Invention Compound III (i.e.,1-(1,3-benzodioxol-5-ylcarbonyl)-1,2,3,6-tetrahydropyridine;alternatively referred to asN-(3,4-methylenedioxybenzoyl)-1,2,3,6-tetrahydropyridine) withaniracetam across a range of dosages on two response size measures. Theinvention compounds are seen to be more potent than aniracetam; e.g., at750 μM, Invention Compound I produces a nine-fold greater increase inthe response area than does aniracetam.

FIG. 3 shows that Invention Compound I increases the magnitude oflong-term potentiation (induced by a standard physiological inductionparadigm) over that obtained in the absence of the compound.

FIG. 4 shows that Invention Compound I slows the decay rate of synapticresponses (a measure of the response duration) recorded in thehippocampal field CA1 of intact rats following peripheral administrationof the compound. Data for eight rats injected intraperitoneally withInvention Compound I are compared with results from seven rats injectedwith the carrier vehicle.

FIG. 5 shows the distribution measured by PET scan of ¹¹C-labelledInvention Compound II in an appropriate carrier in a 200 gram rat afterip injection. Brain uptake is observed to plateau in 5-10 minutes at adistribution approximately one-quarter that of liver, two-thirds that ofheart, and approximately equal to that of the head excluding the cranialcavity.

DETAILED DESCRIPTION OF THE INVENTION

Release of glutamate at synapses at many sites in mammalian forebrainstimulates two classes of postsynaptic receptors usually referred to asAMPA/quisqualate and N-methyl-D-aspartic acid (NMDA) receptors. Thefirst of these mediates a voltage independent fast excitatorypost-synaptic current (the fast epsc) while the NMDA receptor generatesa voltage dependent, slow excitatory current. Studies carried out inslices of hippocampus or cortex indicate that the AMPA receptor-mediatedfast epsc is by far the dominant component at most glutaminergicsynapses under most circumstances. AMPA receptors are not evenlydistributed across the brain but instead are largely restricted totelencephalon and cerebellum. They are found in high concentrations inthe superficial layers of neocortex, in each of the major synaptic zonesof hippocampus, and in the striatal complex [see, for example, Monaghanet al., in Brain Research 324:160-164 (1984)]. Studies in animals andhumans indicate that these structures organize complex perceptual-motorprocesses and provide the substrates for higher-order behaviors. Thus,AMPA receptors mediate transmission in those brain networks responsiblefor a host of cognitive activities.

For the reasons set forth above, drugs that enhance the functioning ofthe AMPA receptor could have significant benefits for intellectualperformance. Such drugs should also facilitate memory encoding.Experimental studies [see, for example, Arai and Lynch, Brain Research,in press] indicate that increasing the size of AMPA receptor-mediatedsynaptic response(s) enhances the induction of long-term potentiation(LTP). LTP is a stable increase in the strength of synaptic contactsthat follows repetitive physiological activity of a type known to occurin the brain during learning.

There is a considerable body of evidence showing that LTP is thesubstrate of memory; for example, compounds that block LTP interferewith memory formation in animals, and certain drugs that disruptlearning in humans antagonize the stabilization of LTP [see, forexample, del Cerro and Lynch, Neuroscience 49:1-6 (1992)]. Recently, Itoet al. (1990) supra, uncovered a possible prototype for a compound thatselectively facilitates the AMPA receptor. These authors found that thenootropic drug aniracetam (N-anisoyl-2-pyrrolidinone) increases currentsmediated by brain AMPA receptors expressed in Xenopus oocytes withoutaffecting responses by y-amino-butyric acid (GABA), kainic acid (KA), orNMDA receptors. Infusion of aniracetam into slices of hippocampus wasalso shown to substantially increase the size of fast synapticpotentials without altering resting membrane properties. It has sincebeen confirmed that aniracetam enhances synaptic responses at severalsites in hippocampus, and that it has no effects on NMDA-receptormediated potentials [see, for example, Staubli et al., in Psychobiology18:377-381 (1990) and Xiao et al., in Hippocampus 1:373-380 (1991)].Aniracetam has also been found to have an extremely rapid onset andwashout, and can be applied repeatedly with no apparent lasting effects;these are valuable traits for behaviorally-relevant drugs.

Without wishing to be bound by any particular theory of action, it ispresently believed to be likely that the major effect of aniracetam isto slow the unusually rapid rate at which AMPA receptors desensitize.The compound also greatly prolongs synaptic responses. This would beexpected if it increased the mean open time of AMPA receptor channels bydelaying desensitization. Indeed, it has been found that aniracetamprolongs the open time of AMPA receptor responses and blocks theirdesensitization in membrane patches excised from hippocampal neurons inculture; the magnitude of the effect corresponds closely to the increasein the duration of synaptic responses (recorded in culture or slices)produced by the drug [Tang et al., Science 254: 288-290 (1991)].Aniracetam may also produce other changes in receptor properties; itcauses a small but reliable decrease in the binding of agonists (but notantagonists) to the receptor [Xiao et al., 1991, supra] and may alsoslightly enhance the conductance of the receptor channel [Tang et al.supra].

Aniracetam is classified as a nootropic drug. Nootropics are proposed tobe “cognitive enhancers” [see Fröstl and Maitre, Pharmacopsychiatry Vol.22:54-100 (Supplement) (1989)] but their efficacy in this regard ishighly controversial. Several nootropics have been tested in slices[see, for example, Olpe et al., Life Sci. Vol. 31:1947-1953 (1982); Olpeet al., Europ. J. Pharmacol. Vol. 80:415-419 (1982); Xiao et al., 1991,supra] and only aniracetam and its near relative(R)-1-p-anisoyl-3-hydroxy-2-pyrrolidinone (AHP) facilitate AMPA receptormediated responses. Hence, whatever effects the nootropics might haveare not mediated by facilitation of fast epsc. It is also the case thatperipheral administration of aniracetam is not likely to influence brainreceptors. The drug works only at high concentrations (˜1.0 mM) andabout 80% of it is converted to anisoyl-GABA following peripheraladministration in humans [Guenzi and Zanetti, J. Chromatogr. Vol.530:397-406 (1990)]. The metabolite, anisoyl-GABA, has been found tohave no aniracetam-like effects.

The conversion of aniracetam to anisoyl-GABA involves a break in thepyrrolidinone ring between the nitrogen and the adjacent carbonyl group,as illustrated below:

In order to overcome the stability problems with aniracetam, and inefforts to provide compounds with improved physiological activity, wehave developed a number of compounds having such improved properties.

Therefore, in accordance with the present invention, there are providednovel compounds having the structure:

wherein:

—Y— is selected from:

wherein y is 3, 4, or 5; or

when —J— is selected from:

 or

—(CR₂)_(x)—, wherein x is 4, 5, or 6,

—C_(x)R_((2x-2))—, when —J— is:

—R is hydrogen or a straight chain or branched chain alkyl group having1-6 carbon atoms;

each —M— is independently selected from:

—C(H)—, or

—C(Z)—, wherein Z is selected from:

—R or

—OR;

wherein M can optionally be linked to Y by a linking moiety selectedfrom —C_(n′)H_(2n′)—, —C_(n′)H_((2n′-1))—, —O— or —NR—, wherein n′ is 0or 1;

each —Y′— is independently selected from:

—O—,

—NR— or

—N═; and

—Z′— is selected from:

—(CR₂)_(z)—, wherein z is 1, 2, or 3, or

—C_(z),R_((2z′-1))—, wherein z′ is 1 or 2, when one —Y′— is —N═, or

—C₂R₂— when both —Y′— are —N═ or both —Y′— are —O—;

with the proviso that when each M is —C(H)—, each Y′ is —O—, and Z′ is—CH₂—, then Y is not —(CH₂)_(4,5)—; or

wherein:

—Y—,

 and —M— are as defined above, or

wherein:

—Y—,

 and —M— are as defined above.

In a presently preferred embodiment of the present invention, —Y— isselected from:

—(CH₂)_(x)—, wherein x is 4 or 5,

—C_(x)H_((2x-2))—, wherein x is 4 or 5, or

 wherein y is 3 or 4.

In another presently preferred embodiment of the present invention, Z′is selected from —CR₂—, —CR₂—CH₂—, —CR═, or —CR═CH—, wherein each R isindependently H or a straight chain or branched chain alkyl group having1-6 carbon atoms, as defined above.

In still another presently preferred embodiment of the presentinvention,

In yet another presently preferred embodiment of the present invention,each Y′ is —O—, and Z′ is —CH₂— or —CH₂—CH₂—. This pattern ofsubstitution is especially preferred when —Y— is selected from one ofthe preferred groups set forth above.

When the aromatic ring is not further substituted with a fusedheterocyclic ring, preferred substituent —NR₂ (i.e., where the ringbears a para-substituent) is —NH(CH₃) or —N(CH₃)₂, while preferredsubstituent —OR (i.e., where the ring bears a meta-substituent) is—OCH₃.

Especially preferred compounds of the present invention have thefollowing structures:

wherein

Y′ is O, N or NR′, Y″, when present, is O, N or NR′, R′ is H or astraight chain or branched chain alkyl group having 1-4 carbon atoms,a=3, 4, 5 or 6, b=an even number between 6-12, inclusive, depending onthe value of “a”, c=1 or 2, d=0, 1 or 3, or the combination of Y′ andC_(c)H_(d)—R′ produces a dialkylamino derivative thereof (wherein adialkylamino group replaces the heterocyclic ring fused to the corearomatic ring).

A specific example of a presently preferred compound is1-(1,4-benzodioxan-5-ylcarbonyl)-1,2,3,6-tetrahydropyridine (referred toherein as Invention Compound I), is shown below:

Another example of a presently preferred compound is(1-(1,3-benzodioxol-5-ylcarbonyl)-piperidine) (referred to herein asInvention Compound II), shown below:

A variant of Invention Compounds I and II, in which thenitrogen-containing heterocycle is replaced with a cyclopentanone orcyclohexanone ring, is expected to be especially metabolically stableand can be synthesized as follows:

The above compound is referred to herein as Invention Compound IV. EC₅₀data for this and a number of other compounds described herein have beendetermined and are presented in the Examples. Additional preferredcompounds of the invention include Invention Compound V (i.e.,(R,S)-1-(2-methyl-1,3-benzodioxol-5-ylcarbonyl)-piperidine, InventionCompound XIV (i.e., 1-(quinoxalin-6-ylcarbonyl)-piperidine, InventionCompound XV (i.e.,N-(4-dimethylamino)benzoyl-1,2,3,6-tetrahydropyridine, and the like.

In accordance with another embodiment of the present invention, thereare provided methods for the preparation of the above-describedcompounds. One such method comprises:

(a) contacting a benzoic acid derivative under conditions suitable toactivate the carboxy group thereof for the formation of an amidetherefrom. This is accomplished, for example, by activating the acidwith carbonyl diimidazole, by producing the corresponding benzoylchloride derivative, and the like. The benzoic acid derivative employedfor the preparation of the above-described compounds typically has thestructure:

 wherein —M—, —Y′—, and Z′ are as defined above; or

 wherein —M—, and —R are as defined above; or

 wherein —Y—, —M— and —A′ are as defined above; and

(b) contacting the activated benzoic acid derivative produced in step(a) with a nitrogen-containing heterocyclic compound of the structure:

 wherein Y is as defined above, wherein said contacting is carried outunder conditions suitable to produce the desired imides or amides (i.e.,aniracetam-like compounds).

Conditions suitable for activating the carboxy group of the benzoic acid(i.e., for the formation of an amide therefrom) can readily bedetermined by those of skill in the art. For example, the benzoic acidcan be contacted with carbonyl diimidazole (see, for example, Paul andAnderson in J. Am. Chem. Soc. 82:4596 (1960)), a chlorinating agent(such as thionyl chloride or oxalyl chloride), or the like, underconditions suitable to produce an activated acid, such as thecorresponding benzoyl chloride derivative. See, for example, March,Advanced Organic Chemistry: Reactions, Mechanisms and Structure,McGraw-Hill, Inc. 1968.

Suitable reaction conditions used to carry out the step (b) condensationare well known to those of skill in the art. The artisan also recognizesthat care is generally taken to carry out such reactions undersubstantially anhydrous conditions.

Another method for the preparation of the compounds of the presentinvention comprises:

(a) contacting a benzoic acid derivative (as described above) with atleast two equivalents of a suitable base in suitable solvent, thencontacting the resulting ionized benzoic acid derivative with pivaloylchloride or a reactive carboxylic acid anhydride under conditionssuitable to produce a mixed anhydride containing said benzoic acid; and

(b) contacting said mixed anhydride produced in step (a) with anitrogen-containing heterocyclic compound (as described above), whereinsaid contacting is carried out under conditions suitable to produce thedesired imides or amides (i.e., aniracetam-like compounds).

Suitable bases contemplated for use in this embodiment of the presentinvention include tertiary amine bases such as triethyl amine, and thelike. Suitable solvents contemplated for use in the practice of thepresent invention include inert solvents such as CH₂Cl₂, alcohol-freeCHCl₃, and the like. Reactive carboxylic acid anhydrides contemplatedfor use in the practice of the present invention include trifluoroaceticanhydride, trichloroacetic anhydride, and the like.

Suitable reaction conditions used to carry out the above-describedreaction are well known to those of skill in the art. The artisan alsorecognizes that care is generally taken to carry out such reactionsunder substantially anhydrous conditions.

Yet another suitable method for the preparation of the compounds of thepresent invention comprises:

(a) contacting 3,4-(alkylenedihetero)-benzaldehyde with ammonia underconditions suitable to form an imine derivative thereof,

(b) contacting the imine produced in step (a) with:

 under conditions suitable to form a benzyloxycarbonyl (BOC) imine,

(c) contacting the product of step (b) with a simple conjugated dienesuch as butadiene under cycloaddition reaction conditions; and

(d) contacting the reaction product of step (c) with a Lewis acid underconditions suitable for Friedel-Crafts acylation to occur.

3,4-(alkylenedihetero)benzaldehydes contemplated for use in the practiceof the present invention include 3,4-(methylenedioxy)benzaldehyde,3,4-(ethylenedioxy)-benzaldehyde, 3,4-(propylenedioxy)benzaldehyde,3,4-(ethylidenedioxy)benzaldehyde, 3,4-(propylenedithio)-benzaldehyde,3,4-(ethylidenethioxy)benzaldehyde,4-benzimidazolecarboxaldehyde,4-quinoxalinecarboxaldehyde, and the like.

Simple conjugated dienes contemplated for use in the practice of thepresent invention include butadiene, 1,3-pentadiene, isoprene, and thelike.

Lewis acids contemplated for use in the practice of the presentinvention are well known in the art and include AlCl₃, ZnCl₂, and thelike. See, for example, March, supra.

Still another suitable method for the preparation of the compounds ofthe present invention comprises:

(a) contacting 2,3-dihydroxy naphthalene with 1,2-dibromoethane in thepresence of base under conditions suitable to produce an ethylenedioxyderivative of naphthalene,

(b) contacting the ethylenedioxy derivative of naphthalene produced instep (a) with a suitable oxidizing agent under conditions suitable toproduce 4,5-ethylenedioxyphthaldehydic acid,

(c) contacting the product of step (b) with anhydrous ammonia underconditions suitable to form an imine, which is then treated with asuitable carbonyl-activating agent (e.g., a carbodiimide such asdicyclohexylcarbodiimide) under cyclization conditions suitable to forman acyl imine, and

(d) contacting the product of step (c) with a simple conjugated dieneunder conditions suitable for cycloaddition to occur.

Suitable oxidizing agents contemplated for use in the practice of thepresent invention include potassium permanganate, and the like.Oxidizing conditions suitable to produce 4,5-ethylenedioxyphthaldehydicacid are described, for example, in Organic Synthesis, Collective Volume2, at page 523 (1943).

Treatment of 4,5-ethylenedioxyphthaldehydic acid with anhydrous ammoniainitially forms an imine, which is then treated with a suitablecarbonyl-activating agent which, under appropriate reaction conditions,promotes cyclization of the intermediate imine to produce an acyl imine.

Suitable reaction conditions used to carry out the above-describedreactions are well known to those of skill in the art. The artisan alsorecognizes that care is generally taken to carry out such reactionsunder substantially anhydrous conditions.

In accordance with yet another embodiment of the present invention,there are provided methods for enhancing synaptic responses mediated byAMPA receptors. The method comprises administering to a subject aneffective amount of a compound having the structure:

wherein:

—Y— is selected from:

wherein y is 3, 4, or 5; or

when —J— is selected from:

—(CR₂)_(x)—, wherein x is 4, 5, or 6,

—C_(x)R_((2x-2))—, when —J— is:

—R is hydrogen or a straight chain or branched chain alkyl group having1-6 carbon atoms;

each —M— is independently selected from:

—C(H)—, or

—C(Z)—, wherein Z is selected from:

—R, or

—OR;

wherein M can optionally be linked to Y by a linking moiety selectedfrom —C_(n′)H_(2n′)—, —C_(n′)H_((2n-1))—, —O— or —NR—, wherein n′ is 0or 1;

each —Y′— is independently selected from:

—O—,

—NR— or

—N═; and

—Z′— is selected from:

—(CR₂)_(z)—, wherein z is 1, 2, or 3, or

—C_(z),R_((2z′-1))—, wherein z′ is 1 or 2, when one —Y′— is —N═, or

—C₂R₂— when both —Y′— are —N═ or both —Y′— are —O—; or

wherein:

—Y— and —M— as defined above, or

wherein:

—Y— and —M— are as defined above.

Invention compounds are demonstrated in the examples which follow to besubstantially more potent than aniracetam in increasing AMPA receptorfunction in slices of hippocampus. For example, Invention Compound I isshown to facilitate induction of maximal long-term potentiation invitro, and to reversibly prolong synaptic responses in the hippocampusfollowing peripheral (i.e., intraperitoneal) injections in anesthetizedrats.

The above-described compounds can be incorporated into a variety offormulations (e.g., capsule, tablet, syrup, suppository, injectableform, etc.) for administration to a subject. Similarly, various modes ofdelivery (e.g., oral, rectal, parenteral, intraperitoneal, etc.) can beemployed. Dose levels employed can vary widely, and can readily bedetermined by those of skill in the art. Typically, amounts in themilligram up to gram quantities are employed. Subjects contemplated fortreatment with the invention compounds include humans, domesticatedanimals, laboratory animals, and the like.

Invention compounds can be used, for example, as a research tool forstudying the biophysical and biochemical properties of the AMPA receptorand the consequences of selectively enhancing excitatory transmission onthe operation of neuronal circuitry. Since invention compounds reachcentral synapses, they will allow for testing of the behavioral effectsof enhancing AMPA receptor currents.

Metabolically stable variants of aniracetam have many potentialapplications in humans. For example, increasing the strength ofexcitatory synapses could compensate for losses of synapses or receptorsassociated with aging and brain disease (e.g., Alzheimer's). EnhancingAMPA receptors could cause more rapid processing by multisynapticcircuitries found in higher brain regions and thus could produce anincrease in perceptual-motor and intellectual performance. As anotherexample, since increasing AMPA receptor-mediated responses facilitatessynaptic changes of the type believed to encode memory, metabolicallystable variants of aniracetam are expected to be functional as memoryenhancers.

Additional applications contemplated for the compounds of the presentinvention include improving the performance of subjects withsensory-motor problems dependent upon brain networks utilizing AMPAreceptors; improving the performance of subjects impaired in cognitivetasks dependent upon brain networks utilizing AMPA receptors; improvingthe performance of subjects with memory deficiencies; and the like.

Accordingly, invention compounds, in suitable formulations, can beemployed for decreasing the amount of time needed to learn a cognitive,motor or perceptual task. Alternatively, invention compounds, insuitable formulations, can be employed for increasing the time for whichcognitive, motor or perceptual tasks are retained. As anotheralternative, invention compounds, in suitable formulations, can beemployed for decreasing the quantity and/or severity of errors made inrecalling a cognitive, motor or perceptual task. Such treatment mayprove especially advantageous in individuals who have suffered injury tothe nervous system, or who have endured disease of the nervous system,especially injury or disease which affects the number of AMPA receptorsin the nervous system. Invention compounds are administered to theaffected individual, and thereafter, the individual is presented with acognitive, motor or perceptual task.

The invention will now be described in greater detail by reference tothe following non-limiting examples.

EXAMPLES Example I Preparation of(R,S)-1-(2-methyl-1,3-benzodioxol-5-ylcarbonyl)-piperidine (V)

The synthesis of 2-methyl-1,3-benzodioxole is conducted by the procedureof Nichols and Kostuba (J. Med. Chem 22:1264 (1979)). A solution of 10.3g (76 mmol) of 2-methyl-1,3-benzodioxole and 21 ml of acetic anhydrideis treated with 3.5 ml BF₃ etherate at 0° C. for 24 hr and at −20° C.for three days. The reaction solution is poured into 250 ml 1M Na₂CO₃and extracted with ether. The ether is dried over Na₂SO₄, then removedunder reduced pressure. Purification and distillation under reducedpressure yields the ketone, 5-acetyl-2-methyl-1,3-benzodioxole.

The above-described ketone is oxidized to the acid by dissolution inaqueous dioxane/NaOH and treatment with Br₂ and iodoform reagent (KI/I₂in aqueous NaOH). Excess halogen is destroyed with Na₂SO₃ and theaqueous solution extracted with CH₂Cl₂, then ether. Acidification of theaqueous solution with conc. HCl yields2-methyl-1,3-benzo-dioxol-5-ylcarboxylic acid, which can be crystallizedfrom CHCl₃/CCl₄/petroleum ether. ¹H NMR δ 1.71 (d, 3, J=5 Hz), 6.36 (q,1, J=5 Hz), 6.81 (d, 1, J=8.2 Hz), 7.46 (d, 1, J=1.6 Hz), and 7.71 ppm(dd, 1, J=1.6, 8.2 Hz).

The above-described acid is coupled to piperidine by first activatingthe acid with a suitable reagent. Specifically, the acid is suspended inCH₂Cl₂ and stirred with one equivalent carbonyl diimidazole (CDI). After30 min, 10% excess piperidine is added. After the reaction is complete(usually less than 1 hr), the solution is extracted with aqueous HCl,water, and aqueous NaHCO₃. The organic solution is dried over Na₂SO₄ andCH₂Cl₂ removed under reduced pressure. Crystallization of the resultingoil by methods known in the art gives(R,S)-1-(2-methyl-1,3-benzodioxol-5-ylcarbonyl)-piperidine (V) as awhite solid. ¹H NMR δ 1.5-1.7 (br m, 6), 1.68 (d, 3, J=5.0 Hz), 6.29 (q,1, J=4.9 Hz), 6.75 (d, 1, J=7.9 Hz), 6.84 (d, 1, J=0.93 Hz), and 6.88(dd, 1, J=8.0, 1.0 Hz).

Example II Alternate Synthesis of(R,S)-1-(2-methyl-1,3-benzodioxol-5-ylcarbonyl)-piperidine (V)

Catechol (11.0 g; 0.100 mol) is dissolved in 50 ml of ether and 29 g offreshly-prepared dioxane dibromide (Yanovskaya, Terent′ev andBelsn′kii), J. Gen. Chem. Vol. 22:1594 (1952)) is added slowly as asolution in 50 ml of ether. The organic solution is washed with water (3times) and dried over MgSO₄. The solvent is removed under reducedpressure to yield 4-bromocatechol as a red-brown oil. ¹H NMR δ 5.52 (s,1), 5.70 (s, 1), 6.74 (d, 1, J=8.74 Hz), 6.92 (dd, 1, J=8.3, 2.3 Hz),and 7.01 ppm (d, 1, J=2.6 Hz).

4-Bromocatechol (18.9 g, 0.100 mol) is dissolved in 200 ml dry tolueneand 20 ml vinyl acetate is added at once, followed by 0.20 g mercuricoxide and 0.4 ml BF₃ etherate. After standing for 10 hr, the solution isextracted with 0.5 M NaOH until the aqueous layer is strongly basic(pH>12). The organic solution is dried over K₂CO₃ and filtered to removethe drying agent. Removal of the toluene under reduced pressure andtreatment of the resulting oil with silica gel in petroleum ether (lowboiling) gives 18 g of (R,S)-5-bromo-2-methyl-1,3-benzodioxole as ayellow oil, ¹H NMR δ 1.67 (d, 1, J=4.78 Hz), 6.27 (q, 1, J=4.72 Hz),6.63 (d, 1, J=8.11 Hz), and 6.88-6.93 ppm (m, 2).

Conversion of the bromoaromatic derivative to the substituted benzoicacid is accomplished by the well-known Grignard reaction (or othersuitable method known in the art). Specifically, the bromoderivative isdissolved in dry tetrahydrofuran and combined with magnesium. Theresulting Grignard reagent is treated with gaseous carbon dioxide. Thereaction solution is quenched with aqueous HCl and the product acid isextracted into ether. The ether solution is extracted with aqueousbicarbonate and the bicarbonate solution is then washed with ether orother suitable organic solvent. The bicarbonate solution is neutralizedwith conc. HCl to yield 2-methyl-1,3-benzo-dioxol-5-ylcarboxylic acid,which can be crystallized from CHCl₃/CCl₄/petroleum ether, as describedabove. The acid is then coupled to piperidine as described above, toproduce the desired product.

Example III Synthesis of1-(1,4-benzodioxan-5-ylcarbonyl)-1,2,3,6-tetrahydropyridine (I)

1,4-benzodioxan-6-carboxylic acid (also known as3,4-ethylenedioxybenzoic acid) was synthesized by the oxidation ofcommercially available 3,4-ethylene-dioxybenzaldehyde with potassiumpermanganate, as described in Org. Syn. 2:538 (1943).

1,4-benzodioxan-6-carboxylic acid (3.0 g; 16.7 mmol) was suspended in 40mL of dichloromethane. The acid dissolved upon addition of 3.7 g (2.2equivalents) of triethylamine. Addition of 2.0 g of pivaloyl chloridewas exothermic, and produced a dense precipitate. The mixture wasstirred at room temperature for about 20 minutes, then 1.52 g of1,2,3,6-tetrahydropyridine was slowly added.

Product was purified by diluting the reaction mixture with an equalvolume of diethyl ether, followed by sequential extractions with 1) 1 MHCl, 2) aqueous sodium bicarbonate, and 3) aqueous sodium carbonate. Theorganic solution was dried over sodium sulfate and potassium carbonate.Removal of solvent on a rotary evaporator gave 4.07 g of a pale yellow,viscous oil. Electron impact mass spectroscopy (EIMS) showed the parention at an m/z value of 245, and a base peak at 163 for the acylium ion.Nuclear magnetic resonance spectroscopy (NMR) at 500 MHz revealedresonances at 6.97 (1H, d, J=1.81); 6.93 (1H, dd, J=8.23, 1.86); 6.87(1H, d, J=8.23); 5.5-5.9 (2H, m); 4.27 (4H, s); 3.4-4.3 (4H, m); and 2.2ppm (2H, br s), relative to TMS.

Example IV Alternate Synthesis of1-(1,4-benzodioxan-5-ylcarbonyl)-1,2,3,6-tetrahydropyridine (I)

Synthesis is performed in the same manner as described for thepreparation of Invention Compound VIII with substitution of1,2,3,6-tetrahydropyridine for 3-pyrroline. EIMS m/z=245 (parent), 163(base), 35, and 107. ¹H NMR δ 2.2 (br s, 2), 3.4-4.3 (m, 4), 4.27 (s,4), 5.5-5.9 (m, 2), 6.87 (d, 1, J=8.23 Hz), 6.93 (dd, 1, J=8.23, 1.86Hz), and 6.97 ppm (d, 1, 1.81 Hz). ¹³C NMR δ 64.27 and 64.44(—OCH₂CH₂O—) and 170.07 ppm (carbonyl).

Example V Preparation of1-(1,3-benzodioxol-5-ylcarbonyl)-1,2,3,6-tetrahydro-pyridine (III)

The product amide is made by the method employed for the preparation ofInvention Compound V, which uses carbonyl diimidazole in order toactivate piperonylic acid, or piperonyloyl chloride (available fromAldrich) can be combined with 1,2,3,6-tetrahydropyridine either in asuitable anhydrous solvent or without solvent. In either case, theisolation of product is performed in the same manner as done forInvention Compound V to give Invention Compound III as a white solid.EIMS m/z=231 (parent, 149 (base), and 121. ¹H NMR δ 2.21 (br s, 2),3.4-4.3 (br m, 4), 5.87 (m, 2), 6.00 (s, 2), 6.83 (d, 1, J=7.84 Hz), and6.92-6.96 (dd and d, 2). ¹³C NMR δ 101.3 (—OCH₂O—) and 169.9 ppm(carbonyl).

Example VI Preparation of1-(1,3-benzodioxol-5-ylcarbonyl)-hexamethyleneimine (VII)

The product amide is made by the same method as employed for thepreparation of Invention Compound V, which uses carbonyl diimidazole inorder to activate piperonylic acid, or piperonyloyl chloride can becombined with hexamethyleneimine in a suitable anhydrous solvent orwithout solvent. In either case, the isolation of product is performedin the same manner as done for Invention Compound V to yield InventionCompound VII as a colorless oil. ¹H NMR δ 1.6 (br m, 6), 1.83 (br m, 2),3.4 (br m, 2), 3.63 (br m, 2), 5.98 (s, 2), and 6.78-6.9 (m, 3).

Example VII Preparation of 1-(1,4-benzodioxan-5-ylcarbonyl)-3-pyrroline(VIII)

1,4-Benzodioxan-6-carboxaldehyde is oxidized to the corresponding acidby the procedure of Shriner and Kleiderer in Organic Syntheses, Coll.Vol. 2:538 (1943). Coupling of the acid with 3-pyrroline is conducted byemploying the same method as employed for the preparation of InventionCompound V, which uses carbonyl diimidazole in order to activate thecarboxylic acid, or any other method known in the art, such as, forexample, activation by the reaction of the triethylammonium salt withtrimethylacetyl chloride. The product is crystallized fromCCl₄/Et₂O/hexanes. EMIS m/z=231 (parent), 163 (base), 135, and 107. ¹HNMR δ 4.25-4.30 (m, 6), 4.43 (br, 2), 5.75 (m, 1), 5.85 (m, 1), 6.88 (d,1, J=8.42 Hz), 7.06 (dd, 1, J=8.38, 2.03 Hz), and 7.09 (d, 1, J=2.05Hz).

Example VIII Preparation of1-(1,3-benzoxazol-6-ylcarbonyl)-1,2,3,6-tetrahydopyridine (IX)

3-Amino-4-hydroxybenzoic acid (1.0 g; 6.5 mmol) is suspended in 3 mldiethoxymethyl acetate and heated to reflux for 45 min. The cooledsolution is diluted with ether and 1.02 g of 1,3-benzoxazol-6-carboxylicacid is collected by filtration. EMIS m/z=163 (parent), 146 (base), and118.

Coupling of 1,3-benzoxazol-6-carboxylic acid with1,2,3,6-tetrahydropyridine is performed in the same manner as describedfor the preparation of Invention Compound V through activation withcarbonyl diimidazole or by activation with other suitable reagents suchas oxalyl chloride. The product can be isolated by the same methods asdescribed for the isolation of Invention Compound V and purified bychromatography on silica gel. EIMS m/z=228 (parent), 146 (base), and118. ¹H NMR δ 2.2 (br, 2), 3.4-4.3 (br m, 4), 5.7-5.95 (br m, 2), 7.52(dd, 1, J=8.39, 1.49 Hz), 7.64 (d, 1, J=8.41 Hz), 7.87 (d, 1, J=1.32Hz), and 8.16 ppm (s, 1.).

Example IX Preparation of 1-(1,3-benzoxazol-6-ylcarbonyl)-piperidine (X)

The amide is prepared by coupling 1,3-benzoxazol-6-carboxylic acid withpiperidine by activation of the acid with carbonyl diimidazole asdescribed for the preparation of Invention Compound V. Dilution of thereaction solution with more CH₂Cl₂ causes the product to precipitate.Purification is achieved by chromatography on silica gel. EMIS m/z=230(parent), 229, 146 (base), and 118. ¹H NMR δ 1.55 (br m, 4), 1.70 (br,2), 3.4 (br, 2), 3.75 (br, 2), 7.48 (dd, 1, J=8.29, 1.22 Hz), 7.62 (d,1, J=8.44 Hz), 7.84 (d, 1, J=1.00 Hz), and 8.15 ppm (s, 1).

Example X Preparation of1-(1,3-benzoxazol-5-ylcarbonyl)-1,2,3,6-tetrahydropyridine (XI)

4-Amino-3-hydroxybenzoic acid is converted into1,3-benzoxazol-5-carboxylic acid by treating with diethoxymethyl acetateas described for the preparation of Invention Compound. IX. EMIS m/z=163(parent), 146 (base), 118, 90, and 63. Coupling of the acid with1,2,3,6-tetrahydropyridine is performed in the same manner as describedfor the preparation of isomeric Invention Compound IX. ¹H NMR δ 2.1-2.4(br, 4), 3.4-4.3 (br m, 4), 5.5-5.95 (br m, 2), 7.45 (dd, 1, J=8.17,1.41 Hz), 7.70 (d, 1, J=0.96 Hz), 7.83 (d, 1, J=8.16 Hz), and 8.18 ppm(s, 1).

Example XI Preparation of 1-(1,3-benzimidazol-5-ylcarbonyl)-piperidine(XII)

5-Benzimidazolecarboxylic acid is coupled to 1,2,3,6-tetrahydropyridineby activation of the acid with carbonyl diimidazole in CH₂Cl₂ plus 10%(v/v) dimethylformamide. Purification is achieved by chromatography onsilica gel. FABMS m/z 455 (parent dimer+1), 228 (parent+1), and 145.

Example XII Preparation of1-(quinoxalin-6-ylcarbonyl)-1,2,3,6-tetrahydropyridine (XIII)

3,4-Diaminobenzoic acid (2.0 g; 13 mmol) is dispersed into 50 mlabsolute ethanol. To the chocolate-brown slurry is added 2.2 g (15 mmol)of glyoxal (40% in water) that has been dissolved in 10 ml of ethanol.The mixture is stirred at room temperature for 24 hr. The lightsand-brown 6-quinoxalinecarboxylic acid is collected by filtration andwashed with ethanol and diethyl ether. EMIS m/z=174 (base), 157, 147,129, and 120.

6-Quinoxalinecarboxylic acid (320 mg; 1.8 mmol) is suspended in 10 mlmethylene chloride. As the suspension is stirred, 2 equivalents oftriethylamine are added, followed by 0.22 ml (1.8 mmol) oftrimethylacetyl chloride. After 15 min, 164 ul (1.8 mmol) of1,2,3,6-tetrahydropyridine is added and the solution is stirredovernight. The solution is diluted with 20 ml of diethyl ether andwashed with 10 ml water followed by 10 ml 10% NaCO₃. The organicsolution is dried over Na₂SO₄/K₂CO₃ and concentrated to a red-brown oil.Purification by chromatography on silica gel (eluted with CCl₄/CHCl₃1:1) gives a pale yellow oil that eventually solidifies. The solid islayered with hexane and finely dispersed by mechanical crushing to yieldpale yellow XIII. EMIS m/z=239 (parent), 157 (base), and 129. ¹H NMR δ2.22 and 2.34 (br, 2), 3.54, 3.94, 3.97, and 4.29 (br, 4), 5.5-6.0 (br,2), 7.85 (dd, 1, J=8.7, 1.3 Hz), 8.15 (d, 1, J=1.6 Hz), 8.18 (br d, 1,J=8.5 Hz), and 8.90 ppm (s, 1).

Example XIII Preparation of 1-(quinoxalin-6-ylcarbonyl)-piperidine (XIV)

The coupling of 6-quinoxalinecarboxylic acid to piperidine isaccomplished in a manner similar to that used for the preparation ofInvention Compound XIII, or by any other method known in the art foractivation of aromatic carboxylic acids, such as, for example,activation by carbonyl diimidazole. ¹H NMR δ 1.56 and 1.73 (br, 6), 3.40(br s, 2), 3.79 (br s, 2), 7.82 (dd, 1, J=8.8, 1.9 Hz), 8.13 (d, 1,J=1.6 Hz), 8.17 (d, 1, 8.6 Hz), and 8.9 ppm (m, 2).

Example XIV In Vitro Physiological Testing

The physiological effects of invention compounds can be tested in vitrowith slices of rat hippocampus as follows. Excitatory responses (fieldEPSPs) are measured in hippocampal slices which are maintained in arecording chamber continuously perfused with artificial cerebrospinalfluid (ACSF). During the 15 minute interval indicated by the horizontalbar in FIG. 1, the perfusion medium is switched to one containing either1.5 mM aniracetam (left panel) or 750 μM of Invention Compound I (rightpanel). Responses collected immediately before (1) and at the end ofdrug perfusion (2) are shown as superimposed inserts in FIG. 1(calibration bars: horizontal 10 milliseconds, vertical 0.5 mV). They-axis of the main graph shows the area of the response before, duringand after drug perfusion, expressed as percent of the baseline value;and each data point represents a single response.

To conduct these tests, the hippocampus was removed from anesthetized, 2month old Sprague-Dawley rats and in vitro slices (400 micrometersthick) were prepared and maintained in an interface chamber at 35° C.using conventional techniques [see, for example, Dunwiddie and Lynch, J.Physiol. Vol. 276: 353-367 (1978)]. The chamber was constantly perfusedat 0.5 ml/min with ACSF containing (in mM): NaCl 124, KCl 3, KH₂PO₄1.25, MgSO₄ 2.5, CaCl₂ 3.4, NaHCO₃ 26, glucose 10 and L-ascorbate 2. Abipolar nichrome stimulating electrode was positioned in the dendriticlayer (stratum radiatum) of the hippocampal subfield CA1 close to theborder of subfield CA3.

Current pulses (0.1 msec) through the stimulating electrode activate apopulation of the Schaffer-commissural (SC) fibers which arise fromneurons in the subdivision CA3 and terminate in synapses on thedendrites of CA1 neurons. Activation of these synapses causes them torelease the transmitter glutamate. Glutamate binds to the post-synapticAMPA receptors which then transiently open an associated ion channel andpermit a sodium current to enter the postsynaptic cell. This currentresults in a voltage in the extracellular space (the field excitatorypost-synaptic potential or field “EPSP” ) which is recorded by a highimpedance recording electrode positioned in the middle of the stratumradiatum of CA1.

For the experiments summarized in FIG. 1, the intensity of thestimulation current was adjusted to produce half-maximal EPSPs(typically about 1.5-2.0 mV). Paired stimulation pulses were given every40 sec with an interpulse interval of 200 msec (see below). The fieldEPSPs of the second response were digitized and analyzed to determineamplitude, half-width, and response area. If the responses were stablefor 15-30 minutes (baseline), test compounds were added to the perfusionlines for a period of about 15 minutes. The perfusion was then changedback to regular ACSF.

Paired-pulse stimulation was used since stimulation of the SC fibers, inpart, activates interneurons which generate an inhibitory postsynapticpotential (IPSP) in the pyramidal cells of CA1. This feed forward IPSPtypically sets in after the EPSP reaches its peak. It accelerates therepolarization and shortens the decay phase of the EPSP, and thus couldpartially mask the effects of the test compounds. One of the relevantfeatures of the feed-forward IPSP is that it can not be reactivated forseveral hundred milliseconds following a stimulation pulse. Thisphenomenon can be employed to advantage to eliminate IPSP by deliveringpaired pulses separated by 200 milliseconds and using the second(“primed”) response for data analysis.

The field EPSP recorded in field CA1 after stimulation of CA3 axons isknown to be mediated by AMPA receptors: the receptors are present in thesynapses [Kessler et al., Brain Res. Vol. 560: 337-341 (1991)] and drugsthat selectively block the receptor selectively block the field EPSP[Muller et al., Science, supra]. Aniracetam increases the mean open timeof the AMPA receptor channel and as expected from this increases theamplitude of the synaptic current and prolongs its duration [Tang et al.Science, supra]. These effects are mirrored in the field EPSP, asreported in the literature [see, for example, Staubli et al.,Psychobiology supra; Xiao et al., Hippocampus supra; Staubli et al.,Hippocampus Vol. 2: 49-58 (1992)]. The same can be seen in thesuperimposed EPSP traces of FIG. 1 (left hand panel) which werecollected before (1) and immediately after (2) the infusion of 1.5 mManiracetam. The drug augmented the amplitude of the response andextended the duration of the response. The latter effect is responsiblefor most of the increase in the area (net current) of the response whichis plotted in the main graph as a function of time before, during, andafter drug infusion. In these tests, as in the published literature,aniracetam has a rapid onset following infusion, and reverses quicklyupon washout.

The right hand panel of FIG. 1 summarizes a typical experiment withInvention Compound I used at 750 μM (i.e., one half the concentration ofaniracetam). The invention compound produced the same qualitativeeffects as aniracetam as shown in field EPSPs collected immediatelybefore and immediately after a 15 minute infusion. As is evident uponinspection of the data in FIG. 1, the magnitude of the effects was muchgreater even though the concentration of invention compound used wasonly 50% of that of aniracetam. The same can be seen in the main graph(FIG. 1, right hand panel), which shows the effects of InventionCompound I on the area of the field EPSPs as a function of time.Invention compound is similar to aniracetam in that it effected a rapidonset of action and was fully reversible upon washout. Comparison of thetwo panels. in FIG. 1 illustrates the extent to which 750 μM ofInvention Compound I was more potent than 1.5 mM aniracetam.

Example XV Generation of Dose-Response Curves and Derived EC₅₀ Valuesfor Invention Compounds and Aniracetam

Invention Compounds I((1-(1,4-benzodioxan-5-ylcarbonyl)-1,2,3,6-tetrahydropyridine), II(1-(1,3-benzodioxol-5-ylcarbonyl)-piperidine), III(1-(1,3-benzodioxol-5-ylcarbonyl)-1,2,3,6-tetrahydropyridine), andaniracetam were assayed in the physiological test system described forthe generation of data presented in FIG. 1. The left panel of FIG. 2shows the effect of each test compound on the amplitude, while the rightpanel shows the effect of each test compound on the area of synapticresponses. Each point is the mean of 2-10 independent determinations.The regression lines were calculated assuming a standard hyperbolicsaturation function.

The invention compounds produced dose-dependent increases in bothmeasures (i.e., in maximum amplitude and response area) and wereeffective at concentrations as low as 100 μM. Invention Compound I atthis dose enhanced the area of the field EPSP by 46±16% (mean and S.D.of 4 experiments). As readily seen upon inspection of FIG. 2, each ofthe three invention compounds was significantly more potent thananiracetam at all dosages tested. For example, Invention Compound I(tested at dosages in the range of 750 μM to 1.5 mM) produced a 6-9times greater effect on response area than did aniracetam at the sameconcentrations.

The percent increase in field EPSP amplitude was determined for avariety of Invention Compounds, and aniracetam, as described above, andused to construct log dose/response curves in order to estimate EC₅₀values for each compound. EC₅₀ values are presented in the followingtable. Where maximal responses could not be obtained due to limitedsolubility of some of the compounds, a maximal response corresponding toan increase of 85% was assumed. The variables set forth in the tablerefer to the following generic structure:

Compound #* Y′ Y″ J a b c d R′ EC₅₀ (mM) aniracetam O — N—C(O) 3 6 1 2 H5 I O O N 5 8 2 3 H 0.5 II O O N 5 10  1 1 H 1.5 III O O N 5 8 1 1 H 0.8IV O O CH—C(O) 3 6 1 1 H 0.9 V O O N 5 10  1 1 CH₃ 1.1 VI O O N 4 8 1 1H 1.2 VII O O N 6 12  1 1 H 4 VIII O O N 4 6 2 3 H 3 IX O N N 5 8 1 0 H4 X O N N 5 10  1 0 H 1.3 XI N O N 5 8 1 0 H 3 XII N NH N 5 8 1 0 H 5XIII N N N 5 8 2 1 H 0.05 XIV N N N 5 10  2 1 H 0.3 XV N(CH₃)₂ — N 5 8 —— — 1.7 XVI O O N—C(O) 3 6 1 1 H 2 *Compounds I, III-V and VII-XIV wereprepared as described above. Compound II(1-(1,3-benzodioxol-5-ylcarbonyl)-piperidine) and Compound VI(1-(1,3-Benzodioxol-5-ylcarbonyl)-pyrrolidine) are known compounds

Example XVI Promotion of Long-Term Potentiation by Invention Compounds

Long-term potentiation (LTP; a stable increase in the EPSP size ofsingle responses after brief periods of high frequency stimulation) waselicited in the CA1 field of hippocampal slices in the absence (see FIG.3, stippled bars, N=6) and in the presence of 1.5 mM of InventionCompound I (see FIG. 3, striped bars, N=5). In the latter case, theamount of potentiation was determined after washing out the testcompound and comparing the response size with that before test compoundinfusion. Data presented in FIG. 3 show the percent increase in the EPSPamplitude (mean and S.D.) at 40, 60, and 90 minutes after LTP induction.

For these studies, field EPSPs in slices of hippocampus were elicited bysingle stimulation pulses and recorded by extracellular electrodes asdescribed in Example II. After collecting responses every 40 seconds for20-30 minutes to establish a baseline, LTP was induced with ten shortbursts of pulses delivered to the CA3 axons; each burst consisted offour pulses separated by 10 milliseconds; the interval between thebursts was 200 milliseconds. This pattern of axon stimulation mimics adischarge rhythm observed in the hippocampus of animals engaged inlearning and is referred to as the “theta burst stimulation paradigm”[see, for example, Larson and Lynch in Science Vol. 232: 985-988(1986)]. Testing with single pulses (one every 40 seconds) is thencarried out for an additional 60-90 minutes to determine the amount ofstable potentiation in the EPSP amplitude. As shown in FIG. 3, the twosecond long period of burst stimulation (i.e., 10 bursts separated by200 milliseconds) increased the size of the field EPSPs in controlslices (stippled bars) by about 25%. The increase in the EPSP size wasstable for the duration of the recording (90 min in the experimentsshown in FIG. 3). Equivalent experiments in rats with chronicallyimplanted electrodes have shown that the increase in EPSP size lasts foras long as stable recordings can be maintained, typically on the orderof weeks (see Staubli and Lynch, in Brain Research 435: 227-234 (1987)).This phenomenon is referred to in the literature as long-termpotentiation (LTP).

To determine the effect of test compound on the induction of LTP, 1.5 mMof Invention Compound I was infused for 15 minutes prior to applicationof theta burst stimulation. Test compound was then washed out until theEPSP half-width (which is changed by test compound, but not by LTP) hadreturned to its pre-treatment level. The amplitude of the field EPSPswas then compared to that observed before infusion of test compound andburst stimulation to determine the amount of LTP. The striped bars inFIG. 3 summarize the results (mean and S.D.) of five experiments. As isevident upon inspection of FIG. 3, the degree of stable long-termpotentiation produced by burst stimulation applied in the presence ofInvention Compound I was nearly twice as large as that induced by thesame stimulation administered in the absence of the drug (p<0.02).

There is much evidence linking long-term potentiation to memoryencoding. Therefore, the data summarized in FIG. 3 provide grounds forpredicting that Invention Compound I will be effective in intact animalsas a memory enhancer.

Example XVII Effect of Intraperitoneally Injected Invention Compound Ion Monosynaptic EPSP Responses in the Rat Hippocampus

Stimulating and recording electrodes were placed in the hippocampus ofanesthetized rats so as to activate and monitor the same synapticresponses as in the slice studies described in Example XV. FIG. 4 showsthe size of the normalized decay time constant of the response (mean±S.E.M.) before and after a single intraperitoneal injection (arrow) ofInvention Compound I (circles, n=8) or cyclodextrin/saline vehicle(diamonds, n=7). The time constant for the decay of the EPSP is ameasure for the duration of the response.

In these experiments, male Sprague-Dawley rats were anesthetized withurethane (1.7 g/kg) and body temperature was maintained at 37° C. withthe use of a heat lamp. A stimulation electrode (two twisted stainlesssteel wires, 150 μm diameter, insulated with teflon) was placedstereotaxically in the trajectory of the Schaffer collateral (SC)pathway from CA3 to CA1 of the hippocampus (coordinates relative toBregma: 3.5 mm P., 3.5 mm L., and 3.0-3.7 mm V). A recording electrode(stainless steel, 150 μm diameter, insulated with teflon) was placed inthe ipsilateral CA1 field (coordinates relative to Bregma: 3.8 mm P.,2.9 mm L., and 2.2-2.8 mm V.), 100-200 μm ventral to theelectrophysiologically-identified CA1 stratum pyramidale (i.e., in thestratum radiatum).

Negative field potentials reflecting dendritic EPSPs evoked by SCstimulation (0.1 ms pulses, 10-100 μA) with paired pulses (inter-pulseinterval of 200 msec; see methodology described in Example XV) wereamplified 500 times and digitized by computer at 20 sec intervalsthroughout each experiment. Test compound (120-180 mg/kg of InventionCompound I in 20% w/v 2-hydroxypropyl-beta-cyclodextrin in 50% salinevehicle) or vehicle (1.5-2.1 g/kg) injections were made i.p. Stablesynaptic responses for 10-60 min before and 60-180 min after injectionwere obtained in all animals used for the analysis shown in FIG. 4. Thetime course of the decay time constant was plotted since theprolongation of EPSP was the most prominent effect of Invention CompoundI in hippocampal slices. Decay time constants were determined by singleexponential fits to the decay phase of the synaptic response andexpressed as a percent of the value obtained during the pre-injectioncontrol period.

As is evident from inspection of FIG. 4, the test compound produced arapid increase in the duration of the synaptic response, and this effectreversed within 60-120 minutes of the injection. The effect of InventionCompound I was somewhat larger for the second (primed) response of thepaired stimulation. The effect on response duration is typical for thisgroup of compounds (cf. responses 1 and 2 in the right panel of FIG. 1).Other manipulations which have been used in slices to modulate synapticresponses in general had little effect on the decay time constant [see,for example, Xiao et al. (1991) supra]. These results indicate thatsufficient amounts of the test compound cross the blood-brain barrier toaugment AMPA receptor functioning in situ, and that test compoundinfluences the response in much the same way as low doses of InventionCompound I directly applied to hippocampal slices. The on-goinghippocampal electroencephalogram was continuously monitored in theseexperiments and in no case did injections of Invention Compound Iproduce electrographic seizures.

Example XVIII Distribution of Invention Compound II afterIntraperitoneal Injection

To be effective, nootrophic drugs, or their active metabolites, mustpass the blood brain barrier or be introduced directly through the bloodbrain barrier. To test the ability of invention compounds to pass theblood-brain barrier, Invention Compound II was labelled with carbon-11.

Radiolabelled Invention Compound II (see the table above) is synthesizedby the following scheme (wherein the numbers in parenthesis refer to thequantity of reagent used, in millimoles):

wherein Ar is aryl (such as methylenedioxybenzene), Im is imidazole(thus, ImHCl is imidazole hydrochloride), and R is an alkyl or alkyleneradical (so that R₂NH is, for example, piperidine). ¹¹C-labelled CO₂ isproduced by cyclotron irradiation and subsequently used in theabove-described synthetic scheme. The time to complete the synthesis isabout 22 min (2 times the half-life of carbon-11). After purification of[¹¹C]II on C₁₈ Sep Pak, 260 μCi was diluted with 20 mg of nonradioactiveII as carrier in a 1-ml solution of 23% propylene glycol and 10% ethanolin physiologically-buffered saline in order to simulate the dosage of100 mg/Kg that was used in behavioral studies. The final 1 ml ofsolution was administered to a 200 g rat under halothane anesthesia(1.4-1.7% in oxygen) by intraperitoneal (i.p.) injection.

Biodistribution of the radiotracer in the body of the rat was monitoredby a positron camera (Scanditronix PC2048-15B) and the time-activitycurves were constructed using a Vax 3500 (Digital Equipment Corporation)and shown in FIG. 5. Four regions of interest were selected: a) liver,upper curve (□); b) heart, second curve from top (♦); c) “soft” ormuscle tissue, third curve from top at 30 min (⋄); d) brain, bottomcurve .

The results presented in FIG. 5 indicate that uptake in liver peakedabout 3 minutes after injection, uptake in heart and brain peaked about5 minutes after injection and uptake in soft tissues peaked about 17minutes after injection. Levels in the liver declined markedly for thefirst 5 minutes after peaking and then more gradually. Levels in theother three tissues declined very gradually after peaking.

Not surprisingly, liver showed the maximum uptake, followed by heart. Ofparticular importance is the fact that uptake in the brain was nearly aseffective as uptake in the heart, and as much as a quarter that ofliver. This demonstrates that Invention Compound II passes freelythrough the blood-brain barrier.

Further, entry of Invention Compound II into its target tissue wasrelatively rapid and stayed in the brain for an extended period. Theseproperties indicate that invention compounds may be administered shortlybefore they are needed, and that frequent readministration may not benecessary.

The invention has been described in detail with reference to particularembodiments thereof. It will be understood, however, that variations andmodifications can be effected within the spirit and scope of theinvention.

We claim:
 1. A compound having the general structure of Formula I:

wherein:

is selected from:

—Y— is selected from:

wherein y is 3, 4, or 5; and

wherein x is 4, 5, or 6; —R is hydrogen or a straight chain or branchedchain alkyl group having 1-6 carbon atoms; each —M— is independentlyselected from: —C(H)— and —C(Z)—, wherein Z is selected from: —R and—OR; one —Y′— is —O— and the other —Y′— is independently selected from—NR— and —N═; and —Z′— is selected from: —(CR₂)_(z)—, wherein z is 1, 2,or 3, and —C_(z′)R_((2z-1))—, wherein z′ is 1 or 2, when one —Y′— is—N═.
 2. A compound according to claim 1 wherein —Y— is

and y is selected from 3 or
 4. 3. A compound according to claim 1wherein —Y— is —C_(x)R_((2x-2))—, and x is selected from 4 or
 5. 4. Acompound according to claim 1 wherein

and x is selected from 4 or
 5. 5. A compound according to claim 1wherein Z′ is selected from —CR₂—, CR₂—CH₂— or —CR═, wherein each R isindependently H or a straight chain or branched chain alkyl group having1-6 carbon atoms.
 6. A compound according to claim 1 wherein

each —M— is —C(H); one —Y′— is —N═ and the other —Y′— is —O—; —Y— isC_(x)R_((2x-2))—, wherein x is 4 and R is H; and —Z′— isC_(z′)R_((2z′-2))—, wherein z′ is 2 and R is H.
 7. A compound having thegeneral structure of Formula II:

wherein:

—R is hydrogen or a straight chain or branched chain alkyl group having1-6 carbon atoms, each —M— is independently selected from: —C(H)— and—C(Z)—, wherein Z is selected from: —R and —OR; one —Y′— is —O— and theother —Y′— is independently selected from —NR— and —N═; R′ is H or astraight or branched chain alkyl group having 1-4 carbon atoms' a is 3,4, 5 or 6; b is an even number between 6-12, inclusive, depending on thevalue of a; c is 1 or 2; d is 0, 1 or
 3. 8. A compound according toclaim 7 wherein Y′ is —N═; Y″ is —O—;

a is 5; b is 8; c is 1; d is 0; and R′ is H.
 9. A compound according toclaim 7 wherein Y′ is —O—; Y″ is —N═;

a is 5; b is 8; c is 1; d is 0; and R′ is H.
 10. A compound according toclaim 7 wherein Y′ is —O—; Y″ is —N═;

a is 5; b is 10; c is 1; d is 0; and R′ is H.
 11. A formulation usefulfor enhancing synaptic responses mediated by AMPA receptors, saidformulation comprising: a compound according to claim 1, and apharmaceutically acceptable carrier.
 12. A method for decreasing theamount of time needed for a mammal to learn a cognitive, motor orperceptual task, or for increasing the time for which a mammal retains acognitive, motor or perceptual task, or for decreasing the quantityand/or severity of errors made by a mammal in recalling a cognitive,motor or perceptual task, said method comprising administering to saidmammal an effective amount of a compound of claim
 1. 13. A method forthe treatment of a subject to enhance synaptic response mediated by AMPAreceptors, said method comprising administering to said subject aneffective amount of a compound of claim
 1. 14. A method according toclaim 13 wherein the performance of said subject is improved ansensory-motor problems or cognitive tasks dependent upon brain networksutilizing AMPA receptors, wherein the strength of memory encoding bysaid subject is improved, or wherein brain functioning is improved insubjects with deficiencies in the number of excitatory synapses or inthe number of AMPA receptors.